1. Field of the Invention
The present invention relates to an antenna means for a portable radio communication device, comprising a radiating first element tuned to a first frequency, the first element having a central longitudinal first axis, first and second ends being a first feed point and a first open end, respectively, and a meander configuration.
Specifically, the invention concerns an antenna means for a hand-portable mobile telephone, which requires a compact and efficient antenna. The inventive antenna means is particularly advantageous when two or more radiating elements are to be combined or when an impedance matching means is required for matching radiating element(s) of the antenna means to transmitter/receiver circuitry of the telephone.
2. Description of the Related Art
A general problem that occurs when the size of an antenna radiator is reduced is a reduction in its relative bandwidth. Helically configured radiators are commonly used when antennas are required to fit in confined volumes with limited height. However, the loops of a helical antenna generate a magnetic field that binds energy, which results in a further reduction of the bandwidth. Also, helical radiators have the problem of strong inter-coupling when two or more radiators are arranged close to each other.
GB-A 2 280 789 discloses an antenna means having multiple turns formed by a conductive radiating element formed on a dielectric substrate. The substrate may be tubular having conductive strips on one side, the strips being joined together along meeting edges of the tubular substrate. In another embodiment, the substrate is flat and has conductor strips deposited on both sides, the strips being joined together by feed-throughs along opposite edges of the substrate. That prior art antenna device has the inherent drawbacks of helical antennas, and is difficult and complicated to manufacture because of the need to provide feed-throughs in the substrate or joining conductors at edges.
Although relatively efficient and compact, there is a great variety of prior art antenna devices that involve the above-mentioned problems due to the use of helical radiators. Such antenna devices are disclosed in, for example, European Patent Applications published under Nos. 0 635 898 A1, 0 593 185 A1, and 0 467 822 A2, PCT Applications published under Nos. WO 94/10720 and WO 95/08199, and U.S. Pat. No. 4,868,576.
In the past, meander antennas have been used when an antenna device is required to have a total length which is short in relation to the wavelength at which an associated transmitter/receiver is operated. DE-A1 31 29 045 discloses a direction finder antenna having, for example, a meander structure. A radiating element thereof has a meandering configuration and is mounted on a dielectric carrier.
DE-A1 31 29 045 is considered to disclose the prior art antenna closest to the invention. The problem to be solved thereby is reducing the height of a direction finder antenna, in particular to render it concealable and mobile. However, it only discloses a meander antenna which has a flat configuration. Moreover, the teachings thereof include improving the bandwidth of the antenna by using a conductor having relatively high resistance, leading to a less efficient antenna. Further, there are no provisions for obtaining a mechanically durable antenna, an antenna suited to fit in a limited volume or an antenna to be combined with other types of antennas.
Another plane meandering antenna element is disclosed in Abstracts of Japan 60 E 1572 (publication No. 6-90108), and includes a meandering dipole and a matching means connected to a coaxial transmission line. A meandering feed arrangement for a helical antenna is disclosed in U.S. Pat. No. 5,298,910. In none of the latter two devices, a transmission line is connected to an end of the meandering conductor.
The pending Swedish Patent Application No. 9601706-6 includes means integrated with the antenna for matching the antenna to circuitry of a hand-portable mobile telephone. A similar matching means is suitable also in the present invention. The above-mentioned Swedish Patent Application is therefore incorporated herein by this reference.